Luminous tile

ABSTRACT

A method for the Continuous gradual stretching and drying of industrial hides and similar products comprises at least one step (a) involving the initial partial drying of the completely wetted hides supplied following a treatment with liquids, such as tanning, retanning or dyeing, until their relative moisture content is reduced to between 45% and 65%, at least one step (b) involving the final stretching of the hides by means of localised mechanical stresses able to recover the shrinkage resulting from the partial drying thereof, characterized in that, after said initial partial drying step (a), at least one intermediate stretching step (c) is performed, followed by intermediate partial drying (d) followed by at least one intermediate stretching step (e) before proceeding to said step (c) involving the final drying and heat-fixing of the hides.

TECHNICAL FIELD

The present invention relates in general to the technical field oftanning and concerns in particular a method for the continuous gradualstretching and drying of industrial hides and similar products,according to the preamble of Claim 1.

The invention also relates to a plant for implementing theabovementioned method, comprising all the features contained in thepreamble of Claim 12.

BACKGROUND ART

It is known that certain industrial hide treatments, such as tanning,retanning and greasing, are performed in the wet, i.e. by means ofimmersing the hides in more or less dense water-based, oil-based orgrease-based liquids, which contain chemical substances of an organic orinorganic nature and have the function of inhibiting bacterial andenzymatic processes or protecting the hides and giving them a specificaesthetic appearance.

After the abovementioned treatments, the wetted hides must be dried andstretched in order to proceed with the subsequent working steps.

It is also known that the surface area of the hides is a factor of vitalimportance for the cost-efficiency of a tannery, in that the price ofthe finished products, for the same final quality, is determined on thebasis of this parameter. Therefore, one of the main objectives oftanneries is that of producing hides having the largest footage orsurface area possible, in a manner which is compatible with the otherqualitative demands.

In the past, in order to perform the stretching operation, traditionalstraight-edge blades were used, said blades requiring a large amount ofeffort on the part of the operators and having a limited effectiveness.

This manual operation has gradually been replaced by other automaticoperations, generally called “setting out”, which are performed, forexample, with wringing machines having spiralled cylinders arrangedopposite each other. Alternatively, the hides may be pressed andstretched by means of presses provided with pairs of felt belts whichact on the hides during the feeding thereof.

Another method for stretching the hides consists in so-called “pasting”,which envisages a paste being deposited on the coarse side of the wettedhides, said paste having the function of making the hides stick toglass, porcelain or metal plates. The hides treated in this way passinto a tunnel drier until they lose a significant proportion of theirmoisture. Once dried, the hides are separated and are in the form offlat sheets, ready for finishing and subsequent processing.

Another method of stretching the hides, known in technical jargon as“toggling”, envisages the use of grippers or clamps applied along theedges of the hides and directed radially towards the outside. The clampsare secured to frames which keep the hides extended while they arepassed through a tunnel drier or along a path in a controlledatmosphere. Optionally, the frames are provided with plates forsupporting the hides in sections which can be separated, as described,for example, in U.S. Pat. No. 2,834,147.

A significant drawback of said known method lies in the fact that theareas affected by the grippers are put under greater stress than thecentral areas, in such a way that they are irreversibly damaged, givingrise to so-called “bubbles” or blisters due to the separation and creepof the fibres with respect to the skin. Moreover, the thickness of thehides is less in the gripped areas than the central areas and thereforevaried stretching and reduction in thickness of the hides occurs, withconsequent lower quality of the finished product.

Another known method, described in French application FR-A-2602795,envisages the use of a pair of flat plates on which respectiveelastically deformable mats, generally made of rubber, are placed. Bycompressing the hides between the mats arranged opposite each other andapplying a longitudinal pulling force to the latter, stretching of thehides by means of friction is achieved. Moreover, hot air, which has thefunction of drying the hides, is directed between the mats.Unfortunately, the heat used for heating the hides also damages therubber mats and therefore limits their working life. Moreover, as theworking temperature cannot exceed certain maximum values, the dryingtime increases, reducing the efficiency of the process.

Said known stretching methods have the drawback of subjecting the hidesto a mechanical stretching action which is concentrated in particularalong the peripheral edge thereof. When acting on said areas, which arethe thinnest areas, it is necessary to restrict the magnitude of thestresses in order to avoid breakage. This restricts the increase in thesurface area and therefore the efficiency of the method.

Moreover, the stresses are not uniformly distributed and, above all, arenot applied towards the centre of the hide, which has the greatestthickness and could therefore allow the greatest stretching.

British patent application GB-A-2236111 describes a method forincreasing the total surface area of chrome-tanned or “wet blue” tannedhides, which envisages the moist hides being placed on a flat surfaceand being subjected to a simultaneous action of longitudinal traction,by means of grippers, and compression, by means of rollers displacedlongitudinally with an alternating motion, which is repeated afterrotation of the hides through about 90° C. This treatment allows anincrease in surface area of about 10%.

However, even this solution, like the preceding solutions, does noteliminate the problem of mechanically stressing the peripheral zones ofthe hides and not achieving a uniform stretching thereof.

Moreover, the application of this method does not allow the fibres ofthe hide to be stretched in the region of its central part and thereforethe liquids absorbed in this zone are retained for longer than in otherzones, increasing the drying times.

A method and a line for stretching hides and other similar products isknown from Italian industrial patent application No. VI2001A000220.

In this known method, the wetted hides supplied following a treatmentwith liquids, such as tanning, retanning, dyeing or the like, arepartially dried, for example by means of setting out, and then stretchedby means of localised mechanical stresses, which are applied indirections substantially perpendicular to the plane of lie of the hidesso as to obtain a predetermined increase in surface area, lastly thehides are partially dried so as to stabilise and heat-fix the stretchedhides. This known method is characterized in that during the stretchingstep, the hides are kept wet with a substantially constant level ofmoistness, while the mechanical stresses are exerted across the entiresurface area of the hides in a substantially uniform manner, without anyconstraint along their peripheral edges in order to obtain a radialstretching action over their entire surface area.

This method allows the hides to be dried in a substantially uniformmanner and results in products of a better quality at a relatively lowcost. However, this method is discontinuous and may therefore be subjectto improvement, especially for the treatment of sheep and goat hides andthin hides in general, for which it is not necessary to use a vacuumdrier. Moreover, the wet stretching of the hides is performed in asingle pass, not exploiting to the full the technological andqualitative potential of this process.

Lastly, the use of a vacuum drier makes it necessary to employ a certainnumber of operators who increase the time and cost of processing.

SUMMARY OF THE INVENTION

The object of the present invention is that of overcoming theabovementioned drawbacks by providing a method and a plant for thecontinuous gradual stretching of hides and similar products which allowsdried products of a high quality to be obtained with extremely lowprocessing times and production costs.

A particular object of the present invention is that of devising amethod and a plant for the continuous gradual stretching of hides andsimilar products which allows a gradual and uniform stretching of thehides to be achieved so as to obtain hides of a substantially constantthickness and softness.

A further particular object is that of designing a plant which allowsthe hides to be dried gradually, stretching them gradually as they losetheir moisture content, with successive stressing cycles, so as toincrease the efficiency of the treatment as desired.

These objects, as well as others which will be more clearly apparenthereinafter, are achieved by a method for the continuous treatment ofindustrial hides and similar products which, according to Claim 1,comprises the removal and transfer of the completely wetted hidessupplied following a treatment with liquids, such as tanning, retanningor dyeing, a step involving predrying the wetted hides so as to reducetheir relative moisture content to a value of between 45% and 65%, atleast one initial wet stretching of the hides by means of localisedmechanical stresses able to recover the loss in footage and softnessresulting from the predrying thereof, at least one intermediate partialdrying step, at least one intermediate partial stretching and softeningstep followed by a final drying of the hides, a final stretching andsoftening of the completely dried hides, and stacking of the completelydried and softened hides on a suitable support.

According to a second aspect of the invention, a plant for implementingthe method according to Claim 1 is envisaged, according to theindependent Claim 12.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention will be more clearlyunderstood in the light of the detailed description of some preferredbut not exclusive embodiments of a method and a plant for the continuousstretching and drying of industrial hides and similar products,illustrated by way of a non-limiting example with the aid of theattached plates of drawings in which:

FIG. 1 shows a flow chart which illustrates the method of gradualstretching and drying of hides according to the invention;

FIG. 2 shows a diagram which illustrates in schematic form thevariations in relative moisture content and percentage elongation of thehides during the various steps of the method according to FIG. 1;

FIG. 3 shows a side view of a first preferred embodiment of a plant forthe gradual stretching and drying of hides for implementing the methodaccording to the invention;

FIG. 4 shows a plan view of the plant according to FIG. 3;

FIG. 5 shows a side view of a second preferred embodiment of a plant forthe gradual stretching and drying of hides for implementing the methodaccording to the invention;

FIG. 6 shows a plan view of the plant according to FIG. 5.

DETAILED DESCRIPTION OF SOME PREFERRED EMBODIMENTS

With reference to the attached drawings, a method and a plant for thecontinuous and gradual stretching of industrial hides and similarproducts according to the invention are shown.

The flow chart shown in FIG. 1 illustrates in schematic form the entiregradual stretching and drying process, with two possible operationalvariants, i.e. the first with a single intermediate cycle and the secondwith two intermediate wet stretching and partial drying cycles.

Obviously, the method may also envisage a greater number of intermediatetreatment cycles without thereby departing from the scope of theinvention.

The first part of the method is common to both variants and envisages afirst step a) in which the hides P are removed from a tanning orretanning drum or from a dyeing or grease-dressing tank, denoted inschematic form by B, with a relative moisture content of between 85% and100%.

In these conditions, the fibres of the hides P are particularly pliableand lend themselves to being stretched with minimal risks of breakageand local damages, significantly reducing the risk of “bubbles” andother local defects.

After being removed, the hides P are subjected to a partial predryingstep b), for example using traditional pressing methods performed with awringing or staking-out machine, essentially formed by a feltwringing/stretching press. This step is regulated in such a way that thehides have a relative residual moisture content with values of between45% and 65%. In this step, the hides are stretched slightly or ratherflattened out so that they can be easily conveyed to the next mechanicalstretching step.

At this point, a step c) is envisaged, involving wet stretching of thehides P by means of localised mechanical stresses applied in directionswhich are substantially perpendicular to the plane of lie of the hides,according to the teachings of e.g. patent application No. VI2001A000220,so as to obtain a predetermined increase in surface area.

Conveniently, during the wet stretching step c), the hides P are kept insubstantially constant relative humidity conditions, corresponding tothe humidity on leaving the partial drying step b). In other words,during this step, the hides must not lose their initial moisture contentso as not to lose their pliability when wet.

In addition to this, it is important that the mechanical stresses aredistributed over the entire surface area of the individual hides in asubstantially uniform manner. It is equally important that the hides aremechanically stressed without applying any constraints, i.e. without anygripper or clamp near their peripheral zones, so as to leave the hidesfree to stretch radially in a substantially uniform manner over theirentire surface area.

The stretching step c) is preferably performed until an increase insurface area or footage of between 2% and 4% is obtained, depending onthe type of wet treatment performed previously.

In a number of practical tests carried out on sheep and goat hides,which had an average thickness of about 1 mm and had been tanned withvegetable tan, an increase in the footage of the hides subjected to themethod according to the invention equal to about 4-5% was obtained,compared to the same hides which had not been wet-treated. In the caseof chrome-tanned bovine hides of greater thicknesses, having a relativemoisture content close to 50%, increases in footage of over 10% wereobtained.

It has been established that by acting on hides having a relativemoisture content of over 65%, no benefit in terms of increase in footageis achieved, while the difficulties of working on the wet hides increasein an unacceptable manner.

Conveniently, the localised mechanical stresses are exerted on bothsides of each hide P at uniformly distributed and substantiallyequidistant points of their surface extension. Preferably, themechanical stresses are imparted by means of tools acting on oppositesides of the hides to be stretched so as to produce substantially radialtensions in localised areas centred on said points.

In a preferred embodiment, the mechanical stresses may be performedusing a staking machine with beating plates, which have tools acting indirections substantially perpendicular to the plane of extension of thehides and a substantially constant beating frequency, applied to thehides which are fed while being retained on their opposite sides by apair of mutually facing, annular, conveyor belts.

Preferably, the operating frequency of the staking machine will bebetween 200 and 1,200 strokes a minute and the feed speed of theconveyor belts is between 2 and 15 m/min.

As shown in schematic form in the left-hand part of FIG. 1, at the endof the wet stretching step c) there follows a step d) involving theintermediate drying and conditioning of the hides in order to reducetheir residual relative moisture content to between 25% and 35% so thatthe hides may still be stretched and pulled easily while remainingrelatively flat.

The hides P, still wet, are then conveyed to a further intermediatestretching step e) using procedures similar to those illustrated forstep c), although in lower relative humidity conditions, so as toundergo a further increase in footage of between 2% and 5%.

Lastly, the gradually stretched hides are conveyed to the final dryingand heat-fixing step f), during which their moisture content falls to afinal relative value of between 7% and 15% and their fibres areheat-stressed so as to stabilise their final footage.

In said condition of almost complete dryness, the hides P are subjectedto a final stretching step g) aimed at stabilising the hides and givingthem the degree of softness and suppleness required by the market.

Following the route along the right-hand side of FIG. 1, the hides P aresubjected to two successive cycles of the type described above, asopposed to a single intermediate drying and stretching cycle.

In particular, downstream of the initial stretching step c), the hides Pare subjected to a first intermediate drying step d₁ until they reach alevel of relative moistness of between 30% and 45%, followed by a firstintermediate stretching step e₁). The hides are then subjected to asecond intermediate drying step d₂) until they reach a value of relativemoistness of between 20% and 30%, followed by a second intermediatestretching step e₂.

In this case also the hides P will be conveyed lastly to a final dryingstage f) in order to be technically dried almost completely, i.e. to alevel of relative moistness of between 7% and 15%.

Lastly, the hides P will be subjected to a final stretching step g)until the footage and degree of softness or “feel” required by themarket is obtained.

It should be noted that the wet stretching and gradual stretching allowsthe effects of the two successive steps to be maximised. Owing to thisgradual way of working, increases in footage of up to about 10% may beobtained compared to traditional methods and methods involving wetstretching in a single pass.

The graph according to FIG. 2 illustrates in schematic form the rangesof variation in the relative moisture content of the hides and therelative stretching during the successive steps of the method in thecase of a single intermediate partial drying cycle followed by partialwet stretching. The successive steps b), c), d), e), f), g) are shown onthe x axes and the maximum and minimum values of relative moisturecontent H₂O % and percentage elongation ΔI/I % are shown on the y axes.

FIGS. 3 to 6 illustrate two examples of embodiment of plants forimplementing the method according to the invention.

In particular, FIGS. 3 and 4 illustrate a first plant, denoted in itsentirety by reference number 1, for implementing the method followed inthe left-hand part of the flow chart shown in FIG. 1.

The plant 1 comprises, in sequence, means 2 for removing and feeding thewetted hides P from an apparatus B for treatment with liquids, such as adrum for tanning, retanning, dyeing or the like. In particular, themeans 2 may be formed by an automatic feeder or a pair of operators inorder to perform step a) of the process.

A drying machine 3 for the initial pressing and predrying of the wettedhides P may be envisaged downstream of the transfer means 2, saidmachine being intended to perform step b) of the process, reducing thelevel of relative moistness from a value of between 85% and 100% to avalue of between 45% and 65%.

By way of a non-limiting example, the machine 3 may be formed by awringing/stretching press, model PRC4 RA 3200, produced by the companyBauce of Trissino (Vicenza). The hides P leaving the machine 3 willpreferably have a level of relative moistness of between 35% and 65%.

A continuous stretching machine 4, which is intended to carry out stepc) of the process—i.e. wet stretching the hides P by means of localisedmechanical stresses acting on opposite sides in directions substantiallyperpendicular to the plane of lie thereof—and is capable of achieving apercentage elongation of between 2% and 4%, may be envisaged downstreamof the predrying machine 3.

By way of an example, the machine 4 may be formed by a staking machinewith beating plates of the type called Syncro 3200 produced by thepresent Applicants, in which the hide conveyor belts are made ofmaterials which are waterproof or water-repellent, and in any casenon-absorbent, so as to prevent the drainage and impregnation of liquidscontained in the hides P being processed.

A device for performing the intermediate step d) of the method isenvisaged downstream of the staking machine 4, said device being formedby an intermediate dryer-conditioner 5, for example of the continuousconditioning tunnel type described in international patent WO-A-01/44517in the name of the present Applicants, and regulated so as to reduce themoisture content to values of between 25% and 30%.

A further intermediate stretching machine, denoted by 4′, similar to thestaking machine 4 and acting in the same conditions but with a lowerlevel of moistness of the hides P, is located downstream of theconditioner 5, for performing step e) of the method, in order to achievea percentage elongation of between 2% and 4%.

A continuous drying/conditioning device 5′, which is similar to thedrying/conditioning device 5 and regulated so as to perform the finaldrying step f), bringing the relative moisture content of the hides P toa value of between 7% and 15%, is envisaged downstream of the stretchingmachine 4′.

A stretching or staking device 4″ which acts on the almost completelydry hides, for implementing step g) of the process, in order to increasethe footage by a further 2-3% and give the hides the degree of softnessrequired by the market, is envisaged downstream of the device 5′.

The hides P are then removed from the staking device 4″ and transferredonto a trestle 6 by means of a traditional stacking device 7, forimplementing step h) of the method.

The hides treated in this way are characterized by a significantincrease in surface area of between 5% and 10% and have a notablequality and softness, without being subject to the mechanical and heatstresses which are typical of traditional methods.

It should be pointed out that the plant for the gradual stretching anddrying of industrial hides, for implementing the method described above,may be inserted into a semiautomatic hide-processing line, for exampleof the type described and claimed in international applicationWO-A-96/15275 in the name of the present Applicants.

The plant illustrated in FIGS. 5 and 6, denoted in its entirety byreference number 1′, differs from that shown in FIGS. 3 and 4essentially in that it envisages, instead of a single intermediatedevice, two intermediate partial drying devices, which are denoted by 5,5′ respectively and regulated so as to reduce the relative moisturecontent to values of between 30% and 45% and 20% and 30%, forimplementing steps d₁) and d₂) of the method, followed by respectiveintermediate wet stretching devices, denoted by 4′, 4″ respectively, forimplementing steps e₁) and e₂) of the method according to the invention.

As in the plant according to FIGS. 3 and 4, a final drying device 5″ forimplementing step f), in order to reduce the relative moisture contentto about 7%-15%, and a final stretching device 4′″ which acts on thealmost completely dry hides, for implementing step g) of the process,resulting in a final percentage elongation of between about 5% and 10%,are located downstream of the intermediate stretching device 4″.

Lastly, in the same way as the example according to FIGS. 3 and 4, astacking device 7, which removes the hides P and deposits them on atrestle 6, for implementing step h) of the method, is envisageddownstream of the stretching device 4′″.

It is pointed out that only two operators, for removing the wetted hidesP from the drum or tank B and transferring them onto the means 2 forfeeding to the press 2, are needed to operate the plant, resulting in asignificant reduction in the number of staff and the processing time.Owing to the method and the plant according to the invention, outputrates of about 100 hides/hour can be achieved with just two people,compared to the 10 people needed in the past using traditional methodsand with lower results in terms of quality.

Assuming an increase in footage of about 7%, it is possible to calculatethe benefit in terms of cost-efficiency obtained with the plant and themethod according to the invention. In the case of a plant with an outputrate of about 100 hides/hour, assuming an average footage of about 50square feet per hide and a working shift of about 8 hours/day, a totalfootage of about 40,000 square feet/day and average daily increase ofabout 2,800 square feet/day is achieved.

Assuming the hides cost an average of about 3.6 Euros/square foot, it ispossible to envisage a saving of over 10,080 Euros/day, allowing thecost of a continuous preparation line according to the invention, with asingle cycle comprising a predrying machine and a staking device, to bepaid off rapidly, i.e. in about 3-4 months.

From the above, it can be understood that the method and the preparationline according to the invention achieve the predetermined objects and,in particular, attention is drawn to the increase in footage with auniform quality and substantially constant final thickness, without anydefects or any risk of damage near the edges of the hide.

The method and the wet preparation line according to the invention maybe subject to numerous modifications and variants, all of which fallwithin the inventive idea described in the accompanying claims.

The instant application is based upon and claims priority of patentapplication no. VI2002A000050, filed on Mar. 20, 2002 in Italy, thedisclosure of which is hereby expressly incorporated here in referencethereto.

1. A method for the continuous gradual stretching and drying ofindustrial hides and similar products, comprising the steps of: removaland transfer of the completely wetted hides supplied following atreatment with liquids, such as tanning, retanning or dyeing; predryingof the wet hides until their relative moisture content is reduced to avalue of between 45% and 65%; initial wet stretching and softening ofthe hides by means of localised mechanical stresses able to recover theloss in footage and softness resulting from the predrying thereof; atleast one intermediate partial drying followed by at least oneintermediate partial stretching and softening; final drying of thehides; final stretching and softening of the completely dried hides;stacking of the completely dried and softened hides on a suitablesupport.
 2. The method according to claim 1, wherein downstream of saidstep of initial wet stretching and softening of the hides when wet, afirst intermediate partial drying step is performed, followed by a firstintermediate partial stretching step, followed by a second intermediatepartial drying step, followed by a second intermediate partialstretching steps, before proceeding to said final drying step and finalstretching and softening of the hides.
 3. The method according to claim1, wherein said step involving the final stretching and softening of thehides takes place in residual relative moisture conditions of between 7%and 15%.
 4. The method according to claim 6, wherein the variation inrelative moisture following each of said intermediate partial dryingsteps is between 10% and 40%.
 5. The method according to claim 1,wherein said partial stretching steps are carried out on wet hides so asto each achieve a percentage increase in the surface area of between 2%and 4% and an overall total percentage increase of between 5% and 10%.6. The method according to claim 1, wherein said intermediate partialstretching step is performed by means of localised mechanical stressesexerted on the opposite sides of the wet hides at uniformly distributedand substantially equidistant points, without constraining the hidesalong their edges, and by positioning a pair of substantiallyimpermeable conveyor belts in between so as to keep the hides wet duringthe staking process.
 7. The method according to claim 6, wherein theoperating frequency of said staking machine is between 200 and 1,200strokes a minute and the feed speed of said pair of conveyor belts isbetween 2 and 15 m/min.
 8. A plant for the gradual wet treatment ofindustrial hides for implementing the method according claim 1,comprising; means for removing and transferring the wetted hides from anapparatus for treatment with liquids, such as a drum for tanning,retanning or the like; a device for the initial partial drying of thewetted hides, regulated so as to reduce the relative moisture content ofthe hides to a value of between 45% and 65%; 1 continuous stretchingdevice for stretching the wet hides by means of localised mechanicalstresses which act on opposite sides in directions substantiallyperpendicular to the plane of lie thereof so as to increase the surfacearea by a value of between 2% and 4%; a device for the final continuousdrying and heat-setting of the hides, intended to reduce the finalrelative moisture content of the hides to between 7% and 15%; wherein,downstream of said initial stretching device, at least one intermediatecontinuous drying device followed by an intermediate continuousstretching device located upstream of said final drying and heat-fixingdevice, so as to achieve a total percentage increase in the surface areaof the hides between 5% and 10%.
 9. A plant according to claim 8,wherein each of said continuous stretching devices is essentially formedby a staking machine with at least one pair of beating plates which areprovided with tools and interact periodically with a substantiallyconstant frequency on the wet hides, at least one pair of conveyor beltsfor the continuous feeding of the hides along their plane of extensionbeing positioned in between.
 10. The plant according to claim 8, whereinsaid pair of continuous conveyor belts are made of impermeable materialsuitable for keeping the hides in substantially constant moistureconditions.
 11. The plant according to claim 10, wherein each of saidpartial drying devices is formed by a continuous drying and conditioningtunnel with a controlled level of humidity and ventilation.